The present invention relates to a digital timer for electronic control of a camera shutter.
Applicant incorporates by reference U.S. Pat. No. 3,785,264 which discloses the state of the art of camera shutters having electronically controlled delay releasers. The apparatus of the present invention is useful with these shutters.
Electronic control of exposure time of a photographic camera shutter as a function of a logarithmically potential already is known in several embodiments. Thus, it is known how to control the exposure time, i.e., to cause de-logarithmization, by applying a potential similar to the object brightness to a diode, the current passing through the diode charging a condenser to a response threshold. Similarly, a timer is known, which comprises several RC circuit stages, of which the potentials are summed into a total potential as disclosed in W. German Patent Application No. 2,214,734 of Werner Holle, published Oct. 4, 1973. This total potential also reaches a threshold after the time interval to be formed. Again, it is known that diodes occasionally involve an appreciable temperature error which must be compensated for, and that the RC circuits require appreciable efforts as regards balancing or equalization. These circuits operate in an analogue manner.
However, digitally operating timers are also known. In a prior art arrangement of this kind, as disclosed in W. German Patent Application No. 2,328,422 of Takahata Hisatoshi et al, published Jan. 3, 1974, the reference times are obtained whenever a binary reducer or divider is excited. Furthermore, a digitally operating timer already has been proposed, which comprises a memory and a decoder which are hooked up to a set of binary dividers or reducers, so that a signal is emitted upon the desired time interval. The first of these timers, however, requires an additional series of binary dividers or reducers, which set must be controlled during the timing process and the second timer requires a memory and hence an appreciable amount of components. Furthermore, as regards both of these digital timers, the desired time interval must be known before triggering.